Self-Assembly and Stability of Hydrogen-Bonded Networks of Bridged Triphenylamines on Au(111) and Cu(111)

Abstract

The adsorption, chemical nature, and self-assembly of diaminotriazinyl- and carboxyl-substituted triphenylamines with dimethylmethylene bridges were studied on Au(111) and Cu(111) at submonolayer coverage by low-temperature scanning tunneling microscopy and density functional theory. On Au(111), both molecules form extended porous honeycomb networks. The geometry of the networks agrees well with density functional theory optimized hydrogen-bonded gas phase structures. Therefore, the self-assemblies on Au(111) are strongly directed by intermolecular hydrogen bond interactions. In contrast, on Cu(111) both molecules aggregate in dense islands owing to the stronger molecule–surface interaction. While the carboxyl substituents partially deprotonate at room temperature on Cu(111), the diaminotriazinyl-substituted triphenylamines adsorb mainly intact. The diaminotriazinyl groups deprotonate gradually at increased adsorption temperatures.

A Spherically Shielded Triphenylamine and Its Persistent Radical Cation

“…[10] Exploiting the rich chemistry of aromatic amines,b ack in the 1980s, Hellwinkel and Melan [11] reported an elegant molecular design resulting from the exhaustive introductiono fb ridging units at the ortho-position of triphenylamine, which forces the originally propeller-shaped scaffold into av irtually planar geometry (Figure 1b). [12] Various types of bridged triphenylamines have been reported to date, [12,13] including carbonyl, [14] ether, [5,15,16] thioether, [17] dimethylmethylene, [18,19] and diphenylmethylene bridges [20] as well as triphenylamines with two fused pentagons. [21] It has been demonstrated that Hellwinkel's design principle can be adopted to stabilize N-centered radicalcations by delocalization of the radical over the planarized p-system.…”

Binary supramolecular networks of bridged triphenylamines with different substituents and identical scaffolds

“…The tip-to-side bonding motif of the DAT head group has two bonding options, which leads to an organisational chirality, where homochiral domains with left-handed and right-handed chirality were observed. 8 In contrast, the homomolecular CDTPA network is symmetric. However, the binary ADTPA+CDTPA network also bears the possibility of organisational chirality, since it has an asymmetric tip-to-tip bonding motif, see Fig.…”

“…The global energy minima are twisted, 3-dimensional configurations due to the preferred out-ofplane tilt of the amino groups (see Ref. [8] for details). In Table S1 we refer to the two structural alternatives as "planar" and "twisted".…”

“…Only one of the two amino groups per DAT unit is involved in the hydrogen bonding. 8 Fig. S2b shows a side view of the binary network.…”

Seeking Out Heterogeneous Hydrogen Bonding in a Self-Assembled 2D Cocrystal of Croconic Acid and Benzimidazole on Au(111)

“…One stratagem that has been developed is to first scrutinize such interactions in a chemical environment without solvent or mixing effects, thereby allowing the system to evolve under the guidance of the most thermodynamically stable interactions between precursor molecules; this can be achieved by letting the two molecules directly interact with each other through self-assembly under ultrahigh vacuum (UHV) on a substrate. − ,, UHV surface deposition experiments allow the precursors to “naturally” self-assemble without solvent, but are of course influenced by the substrate itself. Au(111) substrates have often been shown, however, to have a uniform effect on the potential energy surfaces of adsorbed hydrogen-bonded molecular networks, often creating networks that would be predicted in the absence of surface-adsorbate interactions. ,, This indicates that Au(111) is a useful template for such experiments, and Au(111) further allows for the use of scanning tunneling microscopy (STM) to probe the new crystals and determine their self-assembled structures. − Even though the surface will restrict the molecular assembly by forcing it to occur at the interface, the characterization of any mixed-composition molecular network would indicate a degree of thermodynamically stable interaction between the molecular precursors (vs the interactions among the separate components).…”